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PowerPoint Slideshow about 'Fundamentals of MICROFABRICATION' - ull

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The refractive index of porous Si is lower than for bulk Si: it is inversely proportional to the anodization etch current density. A distributed Bragg reflector (DBR) selectively reflects a band of incident wavelengths and is easily formed in highly doped p-type Si by periodically lowering and raising the etch current density, resulting in a sequence of porous layers with alternating high and low refractive index. Panel a shows an optical image of a 500 × 500 μm2 region irradiated with different overlaid scan patterns, with different doses . The wafer was etched with an alternating high/low current density for 4 s per layer, with a total of 15 bilayers formed. The etch rate is progressively slowed by larger irradiation doses, resulting in thinner porous layers that reflect shorter incident wavelengths. Each dose produces a different reflected color when illuminated with white light, with red/orange colors corresponding to areas of lowest dose. The potential of this approach to form patterned arrays of color pixels and lines for display applications is shown in b, where vertical lines, each 10 μm wide, were irradiated to form alternating red-green-blue stripes. Panels c and d show examples of selectively patterning color reflective areas in which two dragon images appear in different colors, corresponding to different irradiated doses in each area. http://www.pbeam.com/siliconmodification.php